Field of the Invention
This invention relates to structure for hoisting marine craft out of water and, more particularly, to a light weight linkage structure for efficiently lifting a craft and for supporting the craft in an inclined orientation.
Background Art
Marine craft are preferably stored out of water to prevent accumulation of marine life on and deterioration of the submerged portion of the craft hull. Further, it is difficult to secure a craft that is in rough waters which may pound against its mooring and damage the hull. Newer style water craft such as the small sized motorized marine craft are not particularly stable in rough water and in a non-moving standing position and, therefore, of necessity should be stored out of the water. The above reasons warrant the removal of the craft from the water after each use, regardless of the frequency of use. It is therefore desirable to have available a sturdy support through which placement of a craft in, and removal of the craft from, the water can be accomplished quickly and with minimal effort.
An exemplary prior art structure is shown and described in U.S. Pat. No. 4,019,212, to Downer. In Downer, two lifting arms are pivotally attached to an upright frame and carry a lift bed which engages the underside of a boat hull for supporting the boat when in an elevated position.
A structure such as that in Downer has numerous drawbacks. First of all, the lifting arms at all times maintain the boat in a horizontal orientation. Water that has accumulated within the boat will not flow towards a drain port normally provided in the stern portion of the hull bottom or transom and, therefore must be manually bailed out. The only way that Downer could tilt the boat to utilize the drain port would be to incline his base which rests on the bottom of the lake, thereby compromising the stability of the entire structure.
Another problem with the Downer structure is that there is no provision made to keep the bed with associated lifting arms from sinking in the water. If the cable is inadvertently slackened, movement of the lifting arms is unrestrained and they may pivot in a clockwise direction in FIG. 1 to the point that the linkage goes over center and must be manually reoriented.
Many known prior art structures use a parallel organ-type linkage with the pairs of lifting arms being equal in length and the base beams and lifting rails also being equal in length. Such a structure is shown in FIGS. 9-11 of U.S. Pat. No. 2,585,664 to LeMay et al where stop members 78, 79 are required to prevent the lifting arms from being lowered to a point where they would lock up and be incapable of lifting the boat. Due to the stops, the LeMay et al rails are considerably above the lake bottom which creates two additional problems, one being the fact that the lift has to be in deep water in order for the rails to be low enough to permit a boat to ride onto the rails for lifting and, second, the entry end of rails extend out beyond the stern pads 13 so that a boat with a motor will have its center of gravity over the unsupported end of the rails which will tip the lift before the boat can be lifted.
Additionally, it may be difficult to consistently position the craft lengthwise along the bed. The result being that the boat is not properly balanced on the bed and there may be a tendency of the entire structure to shift or tip on the lake bottom under the unbalanced load. The Downer structure along with other known structures are extremely heavy, are in many cases, extremely cumbersome, and are almost impossible for two men, let alone one man, to lift and maneuver into position in the water.
All of the above deficiences detract from the desirability of using the boat lift of Downer or of LeMay et al on a frequent basis. The present invention is specifically directed to overcoming these problems in a novel and simple manner.